Rib support for wing panels

ABSTRACT

An innovative wing structure provides ribs to support skin panels without an attachment between the rib and the stringer free flange or the web. The support is provided by rib shear ties installed directly to the stringer skin flange. The rib incorporates a cut away to allow the stringer to pass through the rib. The composite stringer is an ‘I’ section and is stable under compression, not requiring mechanical methods to prevent rolling over.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to the field of aircraft structural systems and more particularly to a rib structure and attachment system for composite wing panels.

2. Description of the Related Art

In aircraft structures, wing panels, which consist of skins and stringers, react wing bending loads. These loads and the resulting deflections produce upper wing compression buckling and a crushing load on ribs supporting the wing panels. The compression buckling capability for the panel is driven by geometry, rib spacing and stringer spacing. The boundary conditions for the panel are determined by the method of support the rib gives the skin/stringer.

Traditional aluminum panel design as shown in FIG. 1 provided panel support by attaching the rib 10 to the stringer 12 by means of a series of rib bolts 14 between the free flange 16 of the stringers and the associated rib chord flange 18. Skins 20 are attached to the stringer outer flanges 22 using fasteners. An alternative method is to attach a butterfly clip between the stringer web and the rib chord. These attachments provided column stability for the panel and do not let the stringer roll over. These designs are undesirable because it requires installation while the wing box is being built. Drilling holes inside an enclosed wing box presents many challenges and provides a source for costly rework.

Further, if this rib bolt design is applied to a composite wing structure, it creates interlaminar tension problems in the stringer radius. This is a poor load path for composite structure which may require reinforcement methods for the stringer radius adding more cost. The composite wing also needs disbond arrestment fasteners common to the stringer and skin in addition to the rib to stringer attachment.

It is therefore desirable to provide structural elements that provides improved load path for rib support of wing panels. It is further desirable that the structure not require drilling of holes inside an enclosed wing box.

SUMMARY OF THE INVENTION

The present invention provides an innovative structure for the ribs to support the panels without an attachment between the rib and the stringer free flange or the web. The support is provided by rib shear ties installed directly to the stringer skin flange. The rib incorporates a cut away to allow the stringer to pass through the rib. The composite stringer is an ‘I’ section and is designed to be stable under compression, not requiring mechanical methods to prevent rolling over.

This design provides further benefit in that all drilling can be done from outside the wing box facilitating automation, allowing fabrication which is much easier, less costly, and less prone to rework.

The wing skin attachment structure of the present invention provides a rib having shear ties at a surface profile and a plurality of cut aways proximate the shear ties. A plurality of stringers have skin flanges which are engaged by the shear ties and free flanges received through the cut aways. A plurality of fasteners attach the skin flanges to the shear ties. The ribs employed in the present invention further incorporate gussets extending from the shear ties adjacent the cut aways to transfer loads to the rib. In an exemplary embodiment, the fasteners engage a wing skin, the skin flange and the shear tie, the skin flanges incorporate tab outs proximate the shear ties and the free flanges incorporate tab outs proximate the cut aways.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will be better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is an elevation view of an exemplary prior art wing structure showing the rib and wing panel attachment elements;

FIG. 2 is an elevation view of a rib and structural elements for wing panel attachment according to the present invention;

FIG. 3 is a section view along line 3-3 of FIG. 2 providing a plan view of the stinger and rib structure at the elevation of the stringer skin flange; and,

FIG. 4 is a section view along line 3-3 of FIG. 2 providing a plan view of the stinger and rib structure at the stringer free flange.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIG. 2 the present invention provides a wing structure having ribs 30 which are fully shear tied. In the wing skin panels, stringer skin flanges 34 attach to shear ties 32 at an airfoil surface profile created by the rib using bolts or other combination tension/compression load path and disbond arrestment fasteners 33 which also attach the skin 35 for the embodiment shown.

The ribs are stiffened from the lower wing surface to the upper wing surface. To react tension load pull off created by the stringer attachment to the shear ties at the ribs, the ribs have gussets 36 surrounding stringer cut aways 38 to help transfer skin panel attachment loads into the web 40 of the ribs and rib stiffeners 41 while providing pass through of the stringers 42. These gussets act in concert with the rib stiffeners for structural integrity of the ribs in conjunction with reacting the pull off loads. For the embodiment shown in the drawings, the ribs are machined to provide the gussets and cutouts. In alternative embodiments the rib features are created by stamping, casting or forging.

The stringers skin flanges are wide with a profile incorporating some local tab outs 43 at the ribs to accommodate the shear ties as shown in FIG. 3. Using fasteners common to the shear ties and skin attachment provide for disbond arrestment and help with the damage tolerance of the design. This additionally limits the number of fasteners required in the wing box. The stringer free flange 44 is tabbed in at the ribs reducing the size of required cut-outs 38 to allow the rib to get as close to the stringer radius 46 as possible where it sits on the skin flange. This reduces the load the stringer radius is required to react.

The wing skin panel is well supported at the rib so the critical location for buckling is between ribs. The profile of the stringer free flange is tabbed out, as necessary, between the ribs to provide the column stability as shown in FIG. 4. The inter-rib flange portions 48 are tailored to provide the desired structural stability while retaining the weight reduction capability of the designs incorporating the present invention.

Having now described the invention in detail as required by the patent statutes, those skilled in the art will recognize modifications and substitutions to the specific embodiments disclosed herein. Such modifications are within the scope and intent of the present invention as defined in the following claims. 

1. A wing skin attachment structure comprising: a rib having shear ties at a surface profile and a plurality of cut aways proximate the shear ties; a plurality of stringers having skin flanges engaged by the shear ties and free flanges received through the cut aways; and, a plurality of fasteners attaching the skin flanges to the shear ties.
 2. A wing skin attachment structure as defined in claim 1 wherein the rib further incorporates gussets extending from the shear ties adjacent the cut aways to transfer loads to the rib.
 3. A wing skin attachment structure as defined in claim 1 wherein the fasteners engage a wing skin, the skin flange and the shear tie.
 4. A wing skin attachment structure as defined in claim 1 wherein the skin flanges incorporate tab outs proximate the shear ties.
 5. A wing skin attachment structure as defined in claim 1 wherein the free flanges incorporate tab ins proximate the cut aways.
 6. An aircraft wing structure comprising a plurality of ribs each having shear ties at a surface profile and a plurality of cut aways proximate the shear ties; wing panels having skins supported by a plurality of stringers, the stringers having skin flanges engaging the skins and associated shear ties of the ribs, the stringers further having free flanges received through the cut aways in the ribs; a plurality of fasteners attaching the skin flanges to the shear ties.
 7. An aircraft wing structure as defined in claim 6 wherein each rib further incorporates gussets extending from the shear ties adjacent the cut aways to transfer loads to the rib.
 8. An aircraft wing structure as defined in claim 6 wherein the fasteners engage the wing skin, the skin flange and the associated shear tie at each rib.
 9. An aircraft wing structure as defined in claim 6 wherein the skin flanges incorporate tab outs proximate the shear ties.
 10. An aircraft wing structure as defined in claim 6 wherein the free flanges incorporate tab ins proximate the cut aways.
 11. A method of manufacturing an aircraft wing structure comprising the steps of: providing a plurality of ribs having shear ties at a surface profile and a plurality of cut aways proximate the shear ties; attaching a plurality of stringers having skin flanges engaged by the shear ties and free flanges received through the cut aways using a plurality of fasteners attaching the skin flanges to the shear ties.
 12. A method of manufacturing an aircraft wing structure as defined in claim 11 wherein the rib provided further incorporates gussets extending from the shear ties adjacent the cut aways to transfer loads to the rib.
 13. A method of manufacturing an aircraft wing structure as defined in claim 11 wherein the step of attaching the plurality of stringer includes employing the fasteners to engage a wing skin, the skin flange and the shear tie.
 14. A method of manufacturing an aircraft wing structure as defined in claim 11 further comprising the preliminary step of forming the stringers with wing skin flanges incorporating tab outs proximate the shear ties.
 15. A method of manufacturing an aircraft wing structure as defined in claim 11 further comprising the preliminary step of forming the stringers with free flanges incorporating tab ins proximate the shear ties. 